Attenuator



May 31, 1955 F. 'r. WORRELL ATTENUATOR Filed April 16, 1946 INVENTORFRANCIS T. WORRELL ATTORNEY United rates Patent ATTENUATOR Francis '1.Wort-ell, Chicago, Ill., assignor, by mesne assignments, to the UnitedStates of America as represented by the Secretary of the NavyApplication April 16, 1946, Serial No. 662,464

6 Claims. (Cl. 33381) This invention relates in general to attenuatorsand in particular to radio frequency power attenuators.

This invention is applicable in general for attenuating electromagneticenergy and in particular for attenuating electromagnetic energy ofultra-high radio frequency.

The principal object of this invention is to provide a variableattenuator having a low insertion loss.

Other and further objects of this invention will be apparent from thefollowing specification when taken with the accompanying drawing whichis an isometric view of an embodiment of the invention.

The attenuator as shown utilizes the properties of series and parallelconnected elements of wave guide transmission lines, commonly known as aMagic T. Input wave guide 10 feeds power to the magic T junction whichhas low loss branch wave guides 11 and 12 and output wave guide 13. Waveguides 11 and 12 from the T junction to junctions 14 and 15 are low losssections of wave guide and section 12 is one-quarter wave length longerthan section 11. The sections of wave guide 16 and 17 are lossy waveguides, the type used being determined by the amount of attenuationdesired. A lossy wave guide section, as defined in the Bureau of Shipspublication, Radar System Fundamentals, Nav- Ships 900,017, publishedApril 1944, is a wave-guide section having a large attenuation per unitlength. This attenuation is substantially greater than that of astandard wave-guide section. Reflecting plungers 18 and 19 are arrangedto move in the lossy wave guides 16 and 17 and are coupled together bymechanical means 20 so that they can be moved equal amounts in unison byrod 21. Plungers 18 and 19 are initially arranged so that the distance Dis equal to the distance D, this then makes the distance from the Tjunction to plunger 19 onequarter wave length or an odd multiple of onequarter wave length longer that the distance from the T junction toplunger 18. As a result the reflected waves from the plungers willarrive back at the T junction out of phase and will thus combine to goout wave guide 13. As the plungers can be inserted as far as thejunctions 14 and 15, the minimum insertion loss is the loss incurred inhaving the energy travel from the T junction to junctions 14 and 15 andback to the T junction, and as these wave guides (11 and 12) are oflow-loss, the insertion loss is low. The added loss will vary directlywith the distances D and D. Using lossy wave guide of known attenuationcharacteristics for sections 16 and 17 the calibration data can becomputed and an absolute calibration obtained.

It is not intended that this invention be limited to the details asshown as other types of transmission lines of equivalent configurationwill give the same operation, and the input and output can be reversedwithout .afiecting the operation of the attenuator. This invention is tobe limited only by the following claims.

What is claimed is:

1. An electromagnetic wave energy attenuator comprising, a magic Tstructure having input, output and two branch transmission linesextending from a common junction, said transmission lines being arrangedwhere by said input line is electrically in parallel with said twobranch transmission lines and said output line is electrically in serieswith said two branch transmission lines, each of said branchtransmission lines terminating in a lossy section for dissipatingelectromagnetic energy therein, adjustable means in each of said lossysections for reflecting electromagnetic energy toward said commonjunction, and means mechanically coupling said reflecting means in saidbranch arms for adjustment thereof in unison.

2. An electromagnetic wave energy attenuator comprising, a magic Tstructure having input, output and two branch transmission linesextending from a common junction, said transmission lines being arrangedwhereby said input line is electrically in parallel with said two branchtransmission lines and said output line is electrically in series withsaid two branch transmission lines, each of said two branch transmissionlines having a lossy section for dissipating electromagnetic wave energytherein, a reflecting termination within each of said lossy sec tions,the lossy section and the coacting reflecting termination of one of saidtwo branch arms being disposed closer said common junction then thecorresponding elements of the other of said two branch arms by onequarter wave length at the frequency of energy to be attenuated, andmeans for mechanically coupling said reflecting terminations fordisplacement thereof in unison through said lossy sections.

3. An electromagnetic wave energy attenuator comprising a magic Tstructure formed of input, output and two branch recangular wave guidesmutually coupled at and extending from a common junction, said waveguides being arranged whereby said input wave guide is electrically inparallel with said two branch wave guides and said output wave guide iselectrically in series with said two branch wave guides, a first lossywave guide section for dissipating electromagnetic wave energy disposedin the first of said two branch wave guides at a first distance fromsaid common junction, a second lossy wave guide section for dissipatingelectromagnetic wave energy disposed in the second of said two branchWave guides at a second distance greater than said first distance by onequarter wave length measured at the frequency of energy to beattenuated, a first reflecting termination adjustable within said firstlossy wave guide section for reflecting energy toward said commonjunction, a second reflecting termination adjustable within said secondlossy wave guide section for reflecting energy toward said commonjunction, mechanical means joining said first and second reflectingterminations for displacement in unison through said lossy wave guidesections, said second reflecting termination being disposed a distancefrom said common junction greater than the distance of said firstreflecting termination from said common junction by one quarter wavelength measured at the frequency of energy to be attenuated.

4. An electromagnetic wave energy attenuator comprising, in combination,a magic T wave guide assembly having an input arm, a pair of H-planeside arms in parallel therewith and an output E-plane arm in series withsaid side arms, said arms extending from a common junction, said H-planeside arms differing in length by one-quarter wave length of thefrequency of the electromagnetic energy being coupled to said assembly,a section of lossy wave guide terminating each of said H-plane side armsand shorting plungers axially displaceable within said lossy wave guidesections for adjusting the effective lengths thereof and for reflectingincident electromagnetic energy back towards said common junction, saidplungers being interconnected to move in unison thereby to maintain saidelfectivc lengths equal during their adjustment.

5. An electromagnetic wave energy attenuator comprising, in combination,a magic T wave guide assembly having input, output and two branch armsextending from a common junction, said arms being arranged whereby saidinput arm is electrically in parallel with said two branch arms and saidoutput arm is electrically in series with said two branch arms, saidbranch arms difiering in length by one-quarter wave length of theelectromagnetic energy being propagated within said assembly, a sectionof lossy wave guide coupled to the end of each of said branch arms, andmeans for adjusting the eliective lengths of said lossy sections whilemaintaining equality thcrebetween, said last-mentioned means consistingof interconnected shorting plungers disposed within said 'lossy waveguide sections and adapted to move axially in unison to provideshort-circuited terminations for said lossy wave guide sections wherebyelectromagnetic energy coupled to said input arm and subdivided betweensaid two branch arms is equally attenuated by said lossy wave guidesections and reflected back toward said common junction by said shortingplungers appearing thereat as equal amplitude signals in phaseopposition.

6. An electromagnetic wave energy attenuator comprising a magic T waveguide assembly having input, output and two branch arms extending from acommon junction, said arms being arranged whereby said input arm iselectrically in parallel with said two branch arms and said output armis electrically in series with said two branch arms, said branch armsdiffering in length by one-quarter wave length of the electromagneticenergy being propagated in the assembly, a section of lossy wave guideconnected to the end of each of said branch arms, shorting plungerdisposed within each of said lossy wave guide sections for determiningthe effective length of these sections and for reflecting incidentelectromagnetic energy back towards said common junction, said shortingplungers being located at equal distances from the ends of said brancharms and being mechanically interconnected to move in unison wherebyelectromagnetic energy initially coupled to said input arm andsubdivided between said branch arms is equally attenuated by said lossywave guide sections and reflected by said shorting lungers thereby toreappear at said common junction as equal amplitude, out-of-phase signalcomponents for coupling into said output arm.

eferences Cited in the file of this patent UNITED STATES PATENTS2,088,749 King Aug. 3, 1937 2,106,763 Southworth F b. 1, 1938 2,197,123King Apr. 16, 1940 2,438,914 Hansen Apr. 6, 1948 2,498,548 Howard Feb.21, 1950 2,510,016 Fernsler May 30, 1950 2,564,030 Purcell Aug. 14, 19512,593,120 Dicke Apr. 15, 1952

